1. Field of the Invention
The present invention relates to a PDP(Plasma Display Panel), and in particular to a method for forming a discharge sustaining electrode which is capable of sustaining an image formed based on a surface discharge in a certain discharge space when a discharge voltage is supplied in a multiple pair in a display apparatus which uses plasma.
2. Description of the Background Art
Generally, a PDP(Plasma Display Panel) is a plane display apparatus which is capable of displaying a motion picture or a still picture using a gas charge phenomenon and is classified into a 2-electrode type, a 3-electrode type and a 4-electrode type. The 2-electrode type is directed to applying a voltage for an addressing and sustaining operation using 2 electrodes, and the 3-electrode type is directed to a surface discharge type and is switched or sustained based on a voltage applied to an electrode installed at a lateral surface of a discharge cell.
In particular, an electrode formed on an image display side panel is formed of a transparent electrode made of a glass material for implementing a certain transmittivity of visual ray. A non-transparent having a small width for overcoming the problems of the present invention in which the conductivity of a transparent electrode is decreased is used integrally with respect to the transparent electrode.
As the width of a metallic electrode is decreased, the transmittivity is increased, so that the width is an important factor for determining a luminance of a PDP.
FIGS. 1 through 4 illustrate a conventional 3-electrode surface discharge PDP.
FIG. 1 is a perspective view illustrating separated upper and lower substrates, FIG. 2 is a view illustrating an installation of electrodes, and FIG. 3 is a view illustrating a state that an upper substrate is rotated at an angle of 90 for explaining the principle of a discharge.
As shown therein, the conventional 3-electrode surface discharge PDP includes a front substrate 1 which is a display surface of an image, and a rear substrate which is parallel to the front substrate 1.
The front substrate 1 is formed of discharge sustaining electrodes C and S which are formed in a pair form at one pixel for sustaining a light emitting operation of a corresponding cell, a dielectric layer 8 for controlling a discharge current of the discharge sustaining electrodes C and S and insulating the electrodes, and a protection layer 9 formed on the dielectric layer 8 for protecting the dielectric layer 8.
The rear substrate 2 is formed of a partition 3 for forming a plurality of discharge spaces, namely, separating cells, a plurality of address electrodes A for forming a discharge pixel at each portion which is crossed by the discharge sustaining electrodes C and S on the front substrate 1, and a fluorescent layer 5 formed on the both sides of the partition 3 and the rear substrate 2 in the interior of each discharge pixel for thereby emitting a visual ray for implementing an image display during an address display.
In addition, the discharge sustaining electrodes C and S are formed of a scan electrode C and a common electrode C. As shown in FIG. 3, each electrode is formed of an ITO electrode 6 which is formed of a transparent conductive material for enhancing a transmittivity and a bus electrode 7 formed of a metallic material. There is a certain interval between the electrodes C and S. When a discharge voltage is applied to both ends of the ITO electrode 6, a surface discharge is generated in a corresponding discharge space. The bus electrode 7 is formed of a metallic material on the ITO electrode 6 and acts to prevent a voltage drop due to the resistance of a transparent conductive material when current is applied.
The light emitting operation of a certain pixel of the conventional PDP will be now explained.
First, when a discharge start voltage of 150˜300V is applied to the scan electrode S at a corresponding cell, an address discharge is generated between the scan electrode S and the address electrode A for thereby forming a wall electric charge on an inner surface in a corresponding discharge space.
Thereafter, when an address discharge voltage is supplied to the scan electrode S and a corresponding address electrode A, an address discharge is generated between the scan electrode S and the address electrode A.
Namely, an electric field is formed in the interior of a corresponding cell, the electrons of the discharge gases are accelerated, and the accelerated electrons collide with ions. At this time, the ionized electrons collide with neutron particles, so that the neutron particles are ionized into electrons and ions at high speed, whereby the discharge gas becomes a plasma state, and a vacuum infrared ray is formed.
The thusly generated infrared ray excites the fluorescent layer 5 to thereby generate a visual ray, and the thusly generated infrared ray is outputted to the outside via the front substrate 1, so that it is possible to recognize a light emitting operation of a certain cell for thereby implementing an image display.
Thereafter, when a discharge sustaining voltage higher than 150V is supplied to the common electrode of the light emitting cell, a sustaining discharge is generated between the scan electrode S and the common electrode C for thereby sustaining a light emitting operation of the cells.
In the conventional PDP, the discharge sustaining electrodes C and S each formed of the ITO electrode 6 and the bus electrode 7 will be explained in detail.
The ITO electrode 6 is formed of a transparent material having a certain conductivity for implementing a transmittivity of visual ray, so that an electric conductivity is low.
Therefore, when fabricating a large size PDP using the above-described ITO electrode 6, it is impossible to display a certain image due to a voltage drop between the first end and the last end to which the voltage is applied. In order to overcome the above-described problems, the metallic bus electrode 7 having a good conductivity is used. Since the bus electrode 7 had a non-transparent characteristic, it is possible to block light displayed in the discharge space and decrease the entire luminance. Therefore, it is needed to maintain a minimum width.
The conventional bus electrode is formed in a three tier structure of Cr-Cu-Cr. Since this structure is implemented by etching each layer, an etching process is complicated, and an under cutting problem may occur when etching the lower layers, so that the quality of the product is decreased. In order to correct the above-described problems, a single film structure is used.
Preferably, the single film is formed of Al and Ag. An aluminum material is cheap, and the electric conductivity of aluminum is lower than Ag. In the case of using Ag, the fabrication cost is increased.
FIG. 4 illustrates a process for forming the bus electrode 7 using Ag.
Namely, in Step SI1, in a state that the ITO electrode is formed on the front substrate 1, and in Step ST2, a black paste 7a including a black non-pattern pigment is printed at an end portion of the ITO electrode 6, and a drying and firing process is performed. In Step ST3, a white paste 7b including a white Ag powder is printed, and a drying and firing process is performed, so that an Ag material bus electrode 7 is formed. At this time, the thickness of the electrode is 5 μm.
In the case that the thickness of the electrode is too thick, the roughness of the surface of the dielectric layer is decreased for thereby causing a malfunction during the discharge.
The black paste 7a is used for enhancing a contrast of the PDP, and the white paste is used for enhancing the luminance.
However, in the thusly constituted electrode structure, since the conductivity at the black portion is small, when applying a voltage for a discharge, a crack problem may easily occur, so that the reliability of the PDP may be decreased due to an open electrode due to the crack.
In addition, since the bus electrode is formed using black and white pastes, the number of the processes and a tack time are increased, and the fabrication cost is increased. In the conventional art, since more than two time printing processes are required, it is impossible to implement a thickness below 5 μm.